Custom form validators with angular

usage.html

<form name="form">
  <label>
    Password
    <input
      type="password"
      name="password"
      ng-model="password"
      required>
  </label>
  <small class="error" ng-show="form.password.$invalid">
    Please enter a password
  </small>

  <label>
    Password Confirmation
    <input
      type="password"
      name="passwordConfirmation"
      ng-model="passwordConfirmation"
      validate-with="passwordMatcher(value)"
      validate-with-name="passwordMatch"
      ng-disabled="!account.password"
      required>
  </label>
  <small class="error" ng-show="form.passwordConfirmation.$invalid">
    You password confirmation does not match!
  </small>

  {{ form.passwordConfirmation.$error.passwordMatch }}
</form>

validate-with.js

/* global angular */
(function(module) {
  'use strict';

  // SEE: related SO articles
  //      http://stackoverflow.com/questions/14012239/password-check-directive-in-angularjs
  //      http://stackoverflow.com/questions/15060035/invalidate-form-by-custom-component-angularjs
  module.directive('validateWith', function() {
    return {
      require: 'ngModel',
      scope: {
        validateWith: '&',
        validateWithName: '@',
      },
      link: function(scope, elm, attrs, ctrl) {
        scope.validateWithName = scope.validateWithName || 'validateWith';

        var handler = function(value) {
          var isValid = scope.validateWith({value: value});
          ctrl.$setValidity(scope.validateWithName, isValid);
          return isValid ? value : undefined;
        };

        ctrl.$parsers.unshift(handler);
      }
    };
  });

})(angular.module('Auto'));